1. Field of the Invention
This invention relates to a unit for removal of impurities from liquids and to a method for doing so.
2. Description of the Prior Art
Removal of impurities from liquids such as aqueous solutions, particularly, heavy metals present in small quantities in waste water effluent, is an acute problem due to the toxicity of the heavy metals and the increasingly stringent water quality regulations regulating discharge of such materials into water bodies. In many areas, water containing small quantities of heavy metals such as chromium, lead, mercury, cadmium, beryllium, etc. cannot be discharged into municipal sewage systems without removal of the heavy metals to an extremely low level.
For other purposes, filtering of aqueous solutions is not adequate with conventional filtering devices because of the nature of the material to be filtered. For example, ferric hydroxide is a gelatinous solid which is very difficult to filter. Fruit juices containing impurities rendering the solution cloudy are also difficult to filter and clarify.
Liquids such as used motor oils, tallow, etc. are difficult to purify by conventional means.
The removal and recovery of hexavalent chromium from aqueous metal treating baths by contact of the hexavalent chromium with a lead compound to form a water-insoluble lead chromate is disclosed in U.S. Pat. No. 3,493,328. U.S. Pat. No. 3,791,520 also discloses a system for removing chromium anions present in small quantities from waste waters by contacting the waste water stream with a particulate carrier having a water insoluble lead compound adsorbed thereon, the lead compound reacting with the chromium in the waste water stream to form a water-insoluble lead chromate. The system for chromium removal disclosed in U.S. Pat. No. 3,791,520 provides an effective method of chromium removal; however, the flow rate through the system must be closely controlled to prevent "channeling" which results in inadequate removal of the chromium anions from the incoming waste water stream. In an effort to overcome the problems encountered with the unit described in U.S. Pat. No. 3,791,520, the unit disclosed and claimed herein was designed.
The use of chitin and chitosan to remove metal ions from aqueous solutions is known from U.S. Pat. Nos. 3,533,940 and 3,635,818.